我有一个ViewController，它将用户输入保存到CoreData，并在尝试保存后显示MBProgressHUD，以表明保存是否成功。
我有一个AddNewViewController类
class AddNewViewController: UIViewController, UIPickerViewDataSource, UIPickerViewDelegate, UITextFieldDelegate {
@IBOutlet weak var inputErrorMessage: UILabel!
@IBOutlet weak var nameLabel: UILabel!
@IBOutlet weak var amountLabel: UILabel!
@IBOutlet weak var dayPicker: UIPickerView!
@IBOutlet weak var durationPicker: UIPickerView!
@IBOutlet weak var nameTextField: UITextField!
@IBOutlet weak var amountTextField: UITextField!
@IBOutlet weak var notesTextField: UITextField!
//variable to contrain the origin view controller
var originVC: String?
// variables to hold user input
var name: String?
var amount: Double?
var notes: String?
var durationDay: Double?
var durationType: String?
// The days and duration options to display in the pickers
var durationPickerDataSource = ["Day(s)","Week(s)","Month(s)","Year(s)"];
var dayPickerDataSource = ["1","2","3","4","5","6","7","8","9","10","11","12"];
@IBAction func saveButton(sender: AnyObject) {
CoreDataStatic.data.saveIncomeBudgetAndExpenses(originVC!, name: name!, amount: amount, durationDay: durationDay!, durationType: durationType!, notes: notes!)
}
/**
The number of columns in the picker view.
*/
func numberOfComponentsInPickerView(dayPickerView: UIPickerView) -> Int {
return 1
}
/**
The number of items in the picker view. Equal to the number of days(12) and duration options(4) .
*/
func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
if pickerView == durationPicker {
return durationPickerDataSource.count;
}
else {
return dayPickerDataSource.count;
}
}
/**
Gets the titles to use for each element of the picker view.
*/
func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
if pickerView == durationPicker{
durationType = durationPickerDataSource[row]
return durationType
}
else {
durationDay = Double(dayPickerDataSource[row])
return dayPickerDataSource[row]
}
}
/**
Display acknowledgement if the Income, Budget or Fixed Expense saved.
*/
func displayMessage(origin: String) {
var message : String
//Changes the message depending on what the user was trying to save.
if CoreDataStatic.data.saved == true {
message = "\(origin) saved!"
}
else if CoreDataStatic.data.saved == false {
message = "Error: \(origin) failed to save!"
}
else {
message = "Error!"
}
print(message)
//displays acknowledgement for 2 seconds.
/*let acknowledgement = MBProgressHUD.showHUDAddedTo(self.view, animated: true)
acknowledgement.mode = MBProgressHUDMode.Text
acknowledgement.label.text = message
acknowledgement.hideAnimated(true, afterDelay: 2)*/
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
self.durationPicker.dataSource = self;
self.durationPicker.delegate = self;
self.dayPicker.dataSource = self;
self.dayPicker.delegate = self;
}
CoreData类：
struct CoreDataStatic {
static let data = CoreData()
}
public class CoreData {
var appDel : AppDelegate
//Manage a collection of managed objects.
let context : NSManagedObjectContext
//Describes an entity in Core Data.
let incomeEntity : NSEntityDescription
let budgetEntity : NSEntityDescription
let fixedExpenseEntity : NSEntityDescription
//Retrieve data from Core Data with the entity 'Scores'.
let income = NSFetchRequest(entityName: "Income")
let budget = NSFetchRequest(entityName: "Budget")
let fixedExpense = NSFetchRequest(entityName: "FixedExpenses")
//Set the key that needs updating which is always 'score'
let nameKeyToUpdate = "name"
let amountDayKeyToUpdate = "amountDay"
let amountWeekKeyToUpdate = "amountWeek"
let amountMonthKeyToUpdate = "amountMonth"
let amountYearKeyToUpdate = "amountYear"
let durationDayKeyToUpdate = "durationDay"
let durationTypeKeyToUpdate = "durationType"
let notesKeyToUpdate = "notes"
var saved : Bool?
func saveIncomeBudgetAndExpenses(origin: String, name: String, amountDay: Double, amountWeek: Double, amountMonth: Double, amountYear: Double, durationDay: Double, durationType: String, notes: String) {
//saving in enity depending on origin view controller
let entity : NSEntityDescription
if origin == "Income" {
entity = NSEntityDescription.entityForName("Income", inManagedObjectContext: context)!
}
else if origin == "Budget" {
entity = NSEntityDescription.entityForName("Budget", inManagedObjectContext: context)!
}
else {
entity = NSEntityDescription.entityForName("FixedExpenses", inManagedObjectContext: context)!
}
let saveNew = NSManagedObject(entity: entity,
insertIntoManagedObjectContext:context)
// add user input to the relevant entity
saveNew.setValue(name, forKey: nameKeyToUpdate)
saveNew.setValue(amountDay, forKey: amountDayKeyToUpdate)
saveNew.setValue(amountWeek, forKey: amountWeekKeyToUpdate)
saveNew.setValue(amountMonth, forKey: amountMonthKeyToUpdate)
saveNew.setValue(amountYear, forKey: amountYearKeyToUpdate)
saveNew.setValue(durationDay, forKey: durationDayKeyToUpdate)
saveNew.setValue(durationType, forKey: durationTypeKeyToUpdate)
saveNew.setValue(notes, forKey: notesKeyToUpdate)
do {
try context.save()
print("saved")
saved = true
}
catch _ {
print("didnt save")
saved = false
}
AddNewViewController().displayMessage(origin)
}
init(){
appDel = (UIApplication.sharedApplication().delegate as! AppDelegate)
context = appDel.managedObjectContext
incomeEntity = NSEntityDescription.entityForName("Income", inManagedObjectContext: context)!
budgetEntity = NSEntityDescription.entityForName("Budget", inManagedObjectContext: context)!
fixedExpenseEntity = NSEntityDescription.entityForName("FixedExpenses", inManagedObjectContext: context)!
}
}
此代码运行并按预期运行但是当displayMessage（）函数中的注释掉的部分取消注释时，我收到以下错误： ＆＃34;致命错误：在展开可选值＆＃34;
时意外发现nil由于行self.durationPicker.dataSource = self;在覆盖viewDidLoad（）
中任何帮助将不胜感激。
注意*如果我在saveButton函数中调用displayMessage（），代码就会工作，因此不确定为什么在从CoreData类调用消息时它不起作用。
答案 0 :(得分：0)
我不确定这是否是正确的方法，但我找到了解决办法。
创建了一个名为attemptSave的变量（bool），默认为false。
在saveIncomeBudgetAndExpenses try和catch中，trySave更改为true。现在使用if语句在两次按钮点击中调用displayMessage（）函数，以检查attemptSave是否为yes，如果是，则调用函数。